Presently, more than 90% of the mineable copper in the world is obtained by processing copper sulfide minerals. Among the copper sulfide present in minerals, chalcopyrite, bornite, chalcosite, covellite, tennantite and enargite, chalcopyrite are the most relatively abundant species and being therefore the most economically interesting species.
Nowadays, the processing of copper sulfide minerals is built upon technologies based in physical and chemical processes associated to mineral crushing, grinding and flotation, followed by melting-conversion of concentrate and electrolytic refining of metals. In the general practice, more than 80% of copper is produced by the processes that follows the described route—called conventional route—, which is limited to high and medium grade minerals, depending on the specific characteristics of the mineral ores and the mineral processing plants. Due to this fact, there are vast and valuable mineral resources having relatively low mineral grades that are sub-economical when conventional technologies are used and remain unexplored due to the lack of an effective technology for their exploitation.
On the other hand, minerals in which copper is present as oxidized species—readily soluble in acid—are processed using acid leaching processes, followed by solvent extraction processes and metal electrowinning, in which constitutes the hydrometallurgical route for copper obtaining. This route is very attractive due to its lower operational and investment costs when compared to conventional technologies and due to its lower environmental impact. However, the application of this technology is limited to oxidized minerals or to the case of mixed copper sulfide minerals in which the metal is present as secondary sulfides (chalcosite or covellite), which are acid-soluble when a strong microorganism-catalyzed oxidizing agent is present (Uhrie, J L, Wilton, L E, Rood, E A, Parker, D B, Griffin, J B and Lamana, J R, 2003, “The metallurgical development of the Morenci MFL Project”, Copper 2003 Int Conference Proceedings, Santiago, Chile, Vol. VI, 29-39).
In the case of low grade minerals, the only effective technology is their processing in heaps or dumps of ores in which the metal is present as acid-soluble species (oxides) or species that are soluble when bacteria are present (minerals having secondary sulfides such as chalcosite and covellite), which are very rare minerals. Due to this reason, it is essential for sustainable mining expansion to develop a technological break that allows economical processing of minerals having high contents of primary sulfides as chalcopyrite, which are nowadays unexploitable by traditional technologies.
It has been well established that leaching or solubilization of sulfured minerals is favored by the presence of bacteria that oxidize iron and sulfur (see, for instance, the recent review of Rawlings Del.: “Biomineralization of metal-containing ores and concentrates”, TRENDS in Biotechnology, Vol. 21 No. 1, p 38-42, 2003). In the exploitation of these minerals by means of heap or dump leaching at commercial scale using mesophilic microorganisms in the range of 25-45° C., satisfactory recoveries and extraction rates of 85% recovery in 270 days of operation are obtained—for leaching of secondary sulfides as covellite (CuS) and chalcosite (CU2S). In this temperature range, the more widely described bacteria at the moment belongs to genera Acidithiobacillus and Leptospirillum, among which the most common species are A. ferrooxidans, A. thiooxidans, and L. ferrooxidans (Espejo, R T and Romero, J., 1997, “Bacterial community in copper sulfide ores inoculated and leached with solutions from a commercial-scales copper leaching plant”, Applied & Environmental Microbiology, Vol. 63, 4, 183-187).
However, for the case of chalcopyrite (CuFeS2) minerals, known microorganisms show a very low leaching rate, therefore copper fractions recovered from chalcopyrite are considered insignificant in industrial labor. A possible explanation, among many others, is the formation of a film over the surface of chalcopyrite that could stop the copper dissolution process (Tshilombo and Dixon DG, “Mechanism and kinetics of chalcopyrite passivation during bacterial leaching”. Proceedings of Copper 2003, 5th international conference Vol. VI book 1, p 99-116).
High temperatures in the range of 75-80° C. are used to avoid the passivation process and to obtain recoveries that make the process economical (Rawlings Del., “Heavy metal mining using microbes”. Annu Rev Microbiol.; 56:65-91. 2002). For instance, the BioCOP™ process being operated in Chuquicamata, Chile, by Codelco and BHP-Billiton, uses extreme thermophilic microorganisms (archaea) in stirred tanks, as revealed in U.S. Pat. No. 6,110,253 and US 20030167879. The conditions attained in leaching tanks for concentrate leaching are not commercially feasible using mineral processing in vats, heaps, dumps, tailing dams and in situ leaching operations.
In chalcopyrite mineral leaching at industrial scale, many microorganisms have been found; for instance, the use of microorganisms belonging to genera Leptospirillum and Sulfobacillus has been described (Okibe N, Gericke M, Hallberg K B, Johnson D B., “Enumeration and characterization of acidophilic microorganisms isolated from a pilot plant stirred-tank bioleaching operation.” Appl Environ Microbiol. 2003, 69(4):1936-43), however the difficulties found in their isolation, growth and storage make their use complex. Other relevant organisms in bioleaching processes are Acidithiobacillus, which present a large diversity with genome homologies ranging between 60-70% intra species and as low as 20-30% inside the genus. Patent EP0004431 refers to the use of the species Thiobacillus ferrooxidans (now designated as Acidithiobacillus ferrooxidans) for chalcopyrite leaching, with strains that can operate at pH 1.0, but requiring forced aeration. Other examples of this species are strains deposited in the American Type Culture Collection, ATCC 19,859, ATCC 33,020 (Sugio T, et al. “Existence of a hydrogen sulfide:ferric ion oxidoreductase in iron-oxidizing bacteria.” Appl. Environ. Microbiol. 58: 431-433, 1992.), ATCC 23,270, (Abdel-Fattah et al. “Numerical modeling of ferrous-ion oxidation rate in Acidithiobacillus ferrooxidans ATCC 23270: optimization of culture conditions through statistically designed experiments” Acta Microbiol Pol. 2002; 51(3):225-35), etc. However, none of them shows a satisfactory activity with regard to the recovery percentage of copper or the recovery rate thereof.